Marsh spent seven years in the CFO role at DS Smith plc (LON:SMDS) and is also a non-executive director and chair of the audit committee at FTSE 250-listed energy services firm John Wood Group PLC (LON:WG).
DS Smith said Marsh will work with the board to ensure an “orderly transition” as it searches for a replacement.
Analysts at Peel Hunt said Marsh was a "pivotal part" in growing the packaging firm, which was promoted to the FTSE 100 in 2017.
"We do not expect the announcement to represent a change in strategy and we retain our positive stance on the stock," analysts commented.
Shares in DS Smith dipped 2% to 360p while William Hill's stock remained flat at 181.4p on Monday morning.
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